Alternative-fuel vehicles offer the potential for the reduction of pollutants in congested areas such as cities. One of the most promising alternative fuels among the wide variety of possible alternative fuels is compressed natural gas (CNG), and vehicles operating from CNG are currently in operation. The CNG fuel is provided at a fueling station and is filled into pressure tanks on the vehicle at a maximum pressure on the order of 4000-6000 pounds per square inch (psi). The fuel is thereafter gradually fed from the pressure tanks into the engine of the vehicle. It is sometimes necessary to remove the fuel from the vehicle, including the pressure tanks and the fuel-flow system, a process called defueling.
A set of standard requirements and specifications, such as found in NGV (Natural Gas Vehicle) 3.1 and NFPA (National Fire Protection Association) 52, for the operation of such alternative-fuel vehicles has been developed. These standards cover physical structures such as standards for fueling valves, so as to promote rapid adoption of uniform fueling equipment. These standards also cover operating conditions so that the alternative-fuel vehicles meeting the standard will be operable and safe in all normal operating conditions envisioned by those writing the standards. The operating-conditions standards also provide designers with a uniform set of conditions and ranges for which equipment must be designed.
One of the important requirements of NGV 3.1 is that the fuel system must be operable and leak free at pressures of from 2 percent to 150 percent of the rated service pressure, and over a temperature range of from −40° F. to +180° F. The rated service pressure is typically established at about 3600-4000 psi, so that the broadest range of pressure requirements for leak-free operation is from 72 psi (2 percent of 3600 psi) to 6000 psi (150 percent of 4000 psi). Fuel systems using discrete valving elements that meet these operating ranges are available. However, these discrete-element fuel systems may be prone to the development of leaks under some conditions and also have economic disadvantages.
A fill block having an integral one-piece body, designed by employees of Circle Seal Corporation and set forth in U.S. Pat. No. 6,240,909, reduces the potential for leaks by minimizing and removing many of the plumbing runs that constitute possible leak paths, and also reduces assembly and maintenance costs as compared with discrete valving systems. However, this design has shortcomings which render it unsuitable for many applications in alternative-fuel vehicles. Chief among these shortcomings is that the fill block using the integral one-piece body of the '909 patent cannot meet the requirements of NGV 3.1. Specifically, the fill block having the integral one-piece body of the '909 patent cannot function in a leak-free manner over the entire range of pressures and temperatures required by NGV 3.1.
There is accordingly a need for an improved fuel-control system for use in alternative-fuel vehicles. The present invention fulfills this need, and further provides related advantages.